Catalytic cracking process employing silica/alumina cogel catalysts

ABSTRACT

Novel hydrocarbon conversion catalysts and methods for their preparation and use are disclosed. The catalysts are particularly appropriate for the conversion of hydrocarbon feeds to high octane gasoline, while increasing light cycle oil and decreasing heavy cycle oil yield. The catalyst comprises a unique cogelled silica-alumina matrix.

This is a division of application Ser. No. 440,556, filed Nov. 22, 1989,now U.S. Pat. No. 4,988,659, which is a continuation-in-part of U.S.Ser. No. 275,470, filed Nov. 23, 1988, now abandoned.

FIELD OF THE INVENTION

This invention relates to novel hydrocarbon conversion catalysts andtheir supports, methods for their preparation, and use thereof inhydrocarbon conversion processes. More particularly, the presentinvention relates to a high activity, large-pore silica/alumina cogelsuitable for the conversion of hydrocarbon feeds. The cogel may alsoadvantageously incorporated into cracking and hydroprocessing catalysts.

BACKGROUND OF THE INVENTION

Silica, alumina and their amorphous mixtures are well known as catalystsused in hydrocarbon conversion process. The method of preparationclearly controls the resultant activity (such as cracking orisomerization activity), and physical properties (such as pore structureand volume, surface area, density and catalyst strength).Silica/-alumina catalysts such as in the present invention can be used"as is", particularly in reactions that require acidic catalysts, or canoptionally be combined with zeolites, clays or other binders, andinorganic oxides for the cracking of liquid hydrocarbons in crackingreactors such as fluid catalytic crackers.

DESCRIPTION OF RELEVANT ART

Numerous silica/alumina catalyst composites and processes for theirpreparation are described in the patent literature. Silica-aluminacomposites have been used commercially for a variety of hydrocarbonprocessing applications, such as cracking, desulfurization,demetalation, and denitrification.

The variety of manufacturing techniques presented in the art, which havebeen recognized as patentably distinct modifications, attest to the factthat the final catalyst properties are highly dependent upon the precisemethod of manufacture. Such variety, with seemingly subtle differences,is also an indicia of the unpredictability of catalyst manufacturingprocedures in general. The change of a single step to another apparentlyequivalent step may result in a more desirable pore structure, increasedactivity, lower deactivation rates, higher crush strengths or a totallyworthless product. Despite major advantages in the art, as exhibited bygreat numbers of new emerging catalysts, the effect upon the finalcatalyst of changing a single step cannot be predicted with certainty,and thus most catalyst research continues by laborious trial and error.

The prior art teaches a number of ways to prepare these compositionswhich affect the chemical and physical properties of the final catalystcomposition. U.S. Pat. No. 4,499,197, Seese et al., for example,describes the preparation of inorganic oxide hydrogels, and moreparticularly, catalytically active amorphous silica-alumina andsilica-alumina rare earth cogels. The active cogels are prepared byreacting aluminate and silicate solutions to obtain a silica-aluminapregel, and then reacting the pregel with an acidic rare earth and analuminum salt solution with complete mixing. C. J. Plank, Journal ofColloid Science, 2,413 (1947), describes the effect of pH, time, andexchange medium on the porous structure of a silica-alumina gel. U.S.Pat. No. 4,226,743 describes a process for preparing a silica-aluminacatalyst which is dense and attrition resistant. The silica-aluminahydrogel is precipitated at high pH and subsequently reacted withsufficient acid aluminum salt at a pH below 4 to obtain an acidichydrogel slurry. Substantial quantities of clay and/or crystallinealumino-silicate zeolites may be included. U.S. Pat. No. 4,310,441describes large pore silica-alumina gels and a method for producingthem. The silica-alumina gel is derived from a cationic aluminum sourceand also an anionic aluminum source.

The patent literature contains examples that teach and claim specificmethods of silica/alumina matrix and catalyst preparation. Some recentpatents for preparing matrices and FCC catalysts therefrom include: U.S.Pat. No. 4,617,108, Shyr, which purports to teach a process wherecatalyst is prepared by a method comprising preparing hydrogel by mixingan aluminum, ammonium and salt of a strong (pKa<2) acid, and alkalimetal silicate such that the concentration of ammonium is enough to forma hydrogel, separating the hydrogel from solution and calcining it toform acidic silica-alumina. Shyr teaches the combination of this matrixwith clay and zeolite for use in an FCC unit.

U.S. Pat. No. 4,198,319, Alafandi, discloses a process where catalyst isprepared by a method comprising mixing in a slurry a faujasite orsilica-aluminum gel containing 50-70 mole silica, and clay, andspray-drying slurry into a catalyst. Alafandi also shows combinations ofgel with clay and zeolite for use in an FCC unit.

U.S. Pat. No. 4,289,653, Jaffe teaches preparing an extruded catalyst bymixing aluminum sulfate and sulfuric acid with sodium silicate to form asilica sol in an alumina salt solution at pH of 1-3, adding NH₄ OH undersubstantially constant pH of at least 4 to 6; adding more NH₄ OH to forma cogelled mass to pH 7.5-8.5; washing cogelled mass; mulling the masswith peptizing agent, a Group VI-B metal compound and a Group VIII metalcompound to form extrudable dough; extruding; and drying and calcining.

SUMMARY OF THE INVENTION

This invention comprises catalytically-active silica/alumina cogelscapable of hydrocarbon conversion. Specifically, it comprises a catalystbase comprised of high surface area silica/alumina cogel tailored tocontribute to both the activity and octane-enhancing characteristics ofthe catalyst. The invention also comprises a process for preparing thecatalyst and a process for converting hydrocarbonaceous feedstock usingthe catalyst. Among other factors, the catalyst not only convertshydrocarbon feeds to high octane gasoline, but increases the light cycleoil yield and decreaes the heavy cycle oil yield also while improvingthe quality of both.

More specifically, the catalyst composition of this invention comprisesa cogelled, silica-alumina matrix prepared by the method whichcomprises:

a. mixing a silicate solution with an aqueous solution of an acidaluminum salt and an acid, to form an acidified silica sol in saidaluminum salt solution, and adjusting said silica sol/aluminum saltsolution mixture to a pH in the range of about 1 to 4;

b. slowly adding sufficient base with vigorous stirring, to saidacidified silica sol/aluminum salt solution mixture to form a cogelslurry of silica and alumina, and to adjust said slurry to a pH in therange of about 5 to 9;

c. aging said cogel slurry at a temperature of ambient to 95° `C.;

d. adjusting the pH of said cogel slurry to about 5-9;

e. recovering a cogelled mass from said slurry;

f. washing said cogelled mass;

g. adjusting the pH of said cogelled mass to between about 4 and 7, andcontrolling to induce syneresis; and

h. forming said combination into particles.

The catalyst also performs well in combination with known"octane-enhancing" additives, such as H-ZSM-5, to yield an increasedoctane rating of the gasoline fraction.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a graphic representation of the peak diameter of the pore sizedistribution versus the apparent bulk density (ABD) of a catalyst of thepresent invention.

FIG. 2 is a graphic representation of the pore volume versus theapparent bulk density of a catalyst of the present invention.

FIG. 3 is a graphic representation of the the peak diameter of the poresize distribution versus the apparent bulk density (ABD) of another,modified cogel of the present invention.

FIG. 4 is a graphic representation of the pore volume versus theapparent bulk density of another, modified catalyst of the presentinvention.

All the figures illustrate the wide variation in pore size distributionand pore volume obtainable with cogels of this invention (as typified byExamples 1 and 5).

DETAILED DESCRIPTION OF THE INVENTION

The cogel comprising the present invention is preferably composed ofsilica, alumina and their amorphous mixtures. The method of preparationcontrols physical properties, such as pore structure and volume, surfacearea, density and catalyst strength, which in turn governs the resultantactivity such as cracking or isomerization. It must be noted thatseemingly very minor differences in the preparation factors discussedbelow can make significant differences in the make-up and effectivenessfor a particular purpose of the matrix and a catalyst of which it may bea component.

The numerous specific factors that are involved in preparing materialscontaining silica-alumina mixtures include;

1. the mole ratio of silica to alumina;

2. the molar concentrations of the silica and alumina in water;

3. the type and/or source of silica;

4. the type and/or source of alumina;

5. the order of addition of silica and alumina;

6. the pH of the solutions when combined;

7. the pH of the mixture during precipitation;

8. the pH of the mixture after precipitation;

9. the precipitating agent;

10. temperatures throughout the process;

11. mixing rates;

12. presence or absence of aging;

13. presence or absence of syneresis;

14. peptization agent;

15. washing and washing agents;

13. method of drying.

The properties of the composition are highly sensitive to each of thesefactors, and variations among these factors, especially in combination,will greatly influence the particular properties of the final cogelproduced.

This cogel is surprisingly active for the cracking of large molecules,such as in vacuum gas oils, to smaller molecules, such as gasoline, andfinds particular use as the active matrix for catalysts. The olefinicityof the products, as indicated by the C₄ olefin to C₄ total ratio, issurprisingly high. This is indicative of gasoline of high octane.

Besides the cogel itself, the present invention also contemplates aprocess for preparing the amorphous silica-alumina cogel, which can beformed into spheres via spray drying, and then subsequently dried to awater content of less than 5 wt. percent. It is also contemplated thatthe cogel may be incorporated into a multi-component catalyst. Theprocess for preparing the amorphous silica-alumina cogel yields amaterial which is surprisingly versatile with respect to the porevolumes, pore size distributions, and apparent bulk densities,attainable. The cogels can be made in either a batch or a continuousmode.

Among the unique characteristics of the fresh/non-steamed cogel are:

high MAT conversions obtainable between about 55% and 80%;

high surface areas, ranging from about 150 to 450 m² /gm;

N₂ pore volumes ranging from about 0.2 cc/gm to 1.2 cc/gm;

N₂ pore size distribution peak diameter ranging from about 30 Å to 260Å, most pores occurring in the mesopore range of 20 to 500 Å.(Micropores are defined as <20 Å. Macropores are defined as >500 Å. Thispore size distribution allows access into the catalyst of largerhydrocarbon molecules, rendering the present catalyst particularlysuitable for residua applications.)

γ-Al₂ O₃ content of the cogels of less than 20 weight percent, usuallyless than 5 weight percent, after calcining.

The preferred cogel may be further defined as one which, in itsequilibrium state, exhibits a specified activity expressed as a weightpercentage derived from the microactivity test (MAT). It may also bedescribed as one which exhibits a specified selectivity expressed as theratio of C₄ olefins to the total C₄ product as derived by the MAT. Thepreferred MAT activity of the present catalyst is measured by a modifiedASTM D-3907. The ASTM D-3907 procedure provides relative MAT activityfor conversion of a standard feed at standard conditions. We havemodified the procedure by changing conditions and feedstocks as shown inthe Tables. The ratio of the C₄ olefin to the total C₄ productcorrelates well with the octane values of the light gasoline, i.e., thehigher the C₄ olefin to C₄ total ratio, the higher the octane of thelight gasoline. This ratio also suggests that the octane of the heavygasoline will also be improved. For the purposes of this invention,light gasoline is defined as the C₅ fraction up to material boiling atapproximately 265° C. and heavy gasoline as the material boiling fromapproximately 265° C. to 430° C.

The foregoing weight percentage and ratio of C₄ olefins to the total C₄product are the values obtained on a standard feed at 496° C. (925° F.),15 to 16 (weight hourly space velocity), 3 C/O (catalyst to oil weightratio), and calculated on the basis of a pre-equilibrated (as describedabove) catalyst dried at 593° C. (1100° F.) in air.

The preferred cogel can also be categorized as one which, in the courseof extended operation, maintains a level of conversion of at least 40%by weight or volume and, more preferably, of at least 50% by weight,particularly on a Feedstock such as Feedstock A in the Examples.

In a preferred embodiment, the silica-alumina cogelled catalyst isprepared by the steps comprising:

1. adding a silicate solution to an aqueous solution of an acid aluminumsalt, such as aluminum chloride or aluminum sulfate and an acid, such ashydrochloric or sulfuric, but preferably a weak acid such as acetic, toform an acidified silica sol in said aluminum salt solution; the pH ofsaid mixture being in the range of 1 to less than about 4;

2. raising the pH of the mixture by adding base, such as NaOH or NH₄ OH,preferably NH₄ OH, to a pH range of about 5-9;

3. aging the cogelled slurry slurry by time and/or temperaturecombinations;

4. removing the filtrate to recover the cogelled mass;

5. adding an acid, such as nitric, sulfuric, or hydrochloric, butpreferably a weak acid such as acetic acid, to adjust the pH to 4-7 toinduce controlled syneresis. Various combinations of time, temperature,pH and Na⁺ concentration can also be used to induce the desiredsyneresis;

6. spray-drying the cogel mass to form spherical particles;

7. washing either the cogelled hydrogel or the spray-dried particles toreduce the Na₂ O content to less than 1 weight percent.

The mixing steps to make the cogelled slurry can be prepared in either abatch or a continuous mass.

Several definitions and explanations are required to clarify further thesteps comprising the preparation of the cogel. First, the silica soldescribed in Step 1 is preferably defined as a colloidal dispersion orsuspension of the metal oxide in a liquid. In a step 3, cogelled slurryor hydrogel may be described as a coagulated colloid with an imbibedliquid phase. In step 5, "syneresis" refers to molecular rearrangementswhich occur in hydrogels, in particular, silica and silica-aluminahydrogels. These rearrangements consist of condensation reactions amongthe units present in the hydrogels. Any factors which promote or disruptthese reactions affect the structure of the hydrogel and also thestructure of the final dried cogel.

A process parameter critical to the successful creation of the desiredcatalyst is the syneresis of the cogelled mass. Syneresis may be bestdefined or analogized to an aging process in which a composition,particularly a hydrogel, contracts and gives up a liquid, usually water,in the process. This syneresis in the present invention materiallyalters the nature of the cogelled may and therefore the resultingspray-dried cogel catalyst, rendering it uniquely suitable for thepurposes discussed above. For a discussion of syneresis insilica-alumina gels, see C. J. Plank, et al., J. Colloid. Sci., 2 (1947)399, and C. J. Plank, J. Colloid. Sci., 2 (1947) 413, incorporatedherein by reference.

Several factors affect syneresis. Among these are the composition of thehydrogel or gel, the solids concentration of the gel, the pH, time,temperature, [Na⁺ ] and the base exchange medium. Consequently, step 5helps to control the physical and chemical characteristics of thespray-dried co-gel, e.g., pore volume and pore size distribution.Several definitions and explanations are required to clarify further thesteps comprising the preparation of the cogel. First, the silica soldescribed in Step 1 is preferably defined as a colloidal dispersion orsuspension of the metal oxide in a liquid. In step 3, "hydrogel" refersto molecular rearrangements which occur in hydrogels, in particularsilica and silica-alumina hydrogels. These rearrangements consist ofcondensation reactions among the units present in the hydrogels. Anyfactors which promote or disrupt these reaction affect the structure ofthe hydrogel and the structure of the final dried cogel. Aging attemperatures of about 25°-105° C., preferably 60°-90° C., in step 3affects the rate of filtration in step 4 and the physicalcharacteristics of the spray-dried product of step 6. In a lesspreferred embodiment, step 5 may be eliminated. Step 7, washing thecogelled mass or the spray-dried particles, may be accomplished atambient or elevated temperatures, i.e. <100° C., with base exchangemedium such as ammonium acetate, or Al⁺⁺⁺ containing solution to reducethe Na⁺ concentration to less that about 0.5 weight percent. Ammoniumacetate at elevated washing temperatures is particularly effective. Step7 may be done at various points in the procedure after step 2.Generally, the cogelled mass is washed prior to mixing with the zeolite.The gellation, encompassed by step 1 and 2, may be done in a batch orcontinuous manner.

This amorphous silica-alumina cogel catalyst shows high MAT conversionboth as prepared and after steaming. The MAT conversions of the freshcogelled catalyst as prepared ranges from 45 to 80 weight percentconversion, preferably >65%, most preferably >70 weight %. The MATconversion of the steamed materials range from about 40 to ˜65 weightpercent, more preferably >50 weight percent.

As discussed above, it is preferable that the cogelled product isspray-dried after homogenizing the slurry. These particles which areformed by spray-drying may also be exchanged with polyvalent ionssubsequent to spray-drying, more preferably exchanged with rate earthions subsequent to spray-drying.

Other components can be combined with the cogel, for example zeolites(large, intermediate, and/or small pore), sieves, such as Beta, SAPO's,ALPO's etc., clays, modified clays, inorganic oxides, and oxideprecursors, metals, carbon, organic substances, etc. These may be addedin steps 1, 2, 5, and/or 7, above. In addition, other metals may be usedto exchange residual Na₂ O. In these compositions the cogels have beenfound to be excellent matrices for FCC applications, as well asexcellent supports for hydrocracking applications. See U.S. Ser. No.252,236, filed Sep. 30, 1988, incorporated herein by reference.

The spray-dried cogel may be used as a cracking catalyst, particularlywhen used in combination with clays or other binders, and/or with azeolite. In general, in order to employ a cracking catalyst which showshigh levels of activity in a commercial FCC operation, it is preferredto employ a catalyst which, in the course of extended operation,maintains a level of conversion of at least 40% by weight and morepreferably of at least 50% by weight. In this context, the weightpercent conversion represents 100 minus the weight percent of fresh feedboiling above the temperature of 221° C. (430° F.). The weight percentconversion includes the weight percent coke and the weight percent freshfeed boiling below the temperature of 221° C. (430° F.). The conversioncapabilities may be expressed in terms of the conversion produced duringactual operation of the FCC process or in terms of the conversionproduced in standard catalyst activity tests. It is also within thecontemplation of the invention to include the use of the cogel for thein a process for the catalytic cracking of hydrocarbonaceous feedstocks.It finds particular use for processing residuum or incremental residuum,more particularly residuums containing catalyst-contaminating metals.

The following Examples are illustrative of the present invention, butare not intended to limit the invention in any way beyond what iscontained in the claims which follow. The data for Examples 1-5 areshown in Table I.

EXAMPLES EXAMPLE 1

Into a mixing tank, 1.808 lbs. of acetic acid was added to 10.25 lbs. ofdeionized water (DI). 24.173 albs. of aluminum trichloride solution wasadded, which contained 4.38 weight percent aluminum and which had a pHof 1.1. The solution was stirred for ten minutes and had a resultant pHof about 0.44.

Into a different mixing vessel, 10.453 lbs. of a sodium silicatesolution containing 28.7 wt. % SiO₂ with 56.69 lbs. of DI water. Thesolution was mixed for 10 minutes and had a resultant pH of about 10.3.

The sodium silicate solution was slowly pumped into the tank containingthe aluminum trichloride solution. It took 52 minutes to add thesilicate solution; the final solution was clear and had a pH of about 2.The aluminum trichloride solution was stirred vigorously.

A dilute solution of NH₄ OH by adding 13.48 lbs. of NH₄ OH, whichcontained 28 wt. % NH₃ to 43.28 lbs. of DI H₂ O. The NH₄ OH solution wasslowly pumped into the silica-, alumina-, acetic acid solution, withvigorous mixing, until a pH of 8 was reached. It took approximately 57minutes to add the NH₄ OH. The ammonium hydroxide addition rate must besufficiently slow to prevent the contents of the vessel fromhydrogelling too quickly.

The resulting slurry was stirred for 3 hours and the final pH wasreadjusted to 8, if necessary. The slurry was filtered at roomtemperature.

The filter cake was washed with a solution of 1.18 lbs. of NH₄ HCO₃dissolved in 30 liters of water (DI). This wash was repeated three moretimes. It was then washed once with 30 liters of water (DI).

The dried and washed cogelled mass was then divided into severalbatches, A-E, for further treatment and spray drying.

Batch A: 600 mls. of water (DI) was added to 4100 grams of cogelledmass. The mixture was homogenized. Its pH was about 8.1. The mixture wasthen spray dried.

Batch B, C, D: 62 grams of acetic acid was added to 8,679.04 grams ofthe cogelled mass (LOI˜90 wt. %) to reduce the pH to about 5.42 andinduce syneresis. 22 additional grams of acetic acid were added toreduce further the pH to 4.83. The mixture was then homogenized, afterwhich ammonium hydroxide was added to raise the pH to 5.59.

Batch B was aged at ambient temperature for 1 hour. The pH was 5.59.

Batch C was aged at ambient temperature for 4 hours. The pH was 5.61.

Batch D was aged at ambient temperature for 24 hours. The pH was 5.81.

Batch E: 50 grams of acetic acid was added to 4544 grams of the cogelledmass (LOI˜90) to adjust the pH to 5.58. An additional 28 grams of acidwas added to reduce the pH further to 5.21, and finally 19 grams morewas added to reduce the pH to 4.85. The mixture was constantlyhomogenized. The pH was then raised to 5.58 by adding ammoniumhydroxide. The material was again homogenized, screened, and aged atambient conditions for 24 hours.

These materials were all spray dried to form an attrition resistantsolid cogel catalyst.

EXAMPLE 2

Additional cogel catalyst samples were prepared as in Example 1, allusing the syneresis step as in Batch E. The materials were spray driedat various spray drying conditions to form Batches F, G, H, I, and J.The results are shown in Table I.

                                      TABLE I                                     __________________________________________________________________________            Example 1      Example 2      Example                                                                            Example                                                                            Example                       MATERIAL                                                                              A  B  C  D  E  F  G  H  I  J  3    4    5                             __________________________________________________________________________    Surface Area                                                                          317                                                                              311                                                                              312                                                                              326                                                                              355                                                                              378                                                                              373                                                                              385                                                                              367                                                                              374                                                                              342  322  371                           Pore Size Dist.                                                                       149                                                                              37 37 35 133                                                                              49 43 89 43 41 59   79   179                           Pore Volume                                                                           0.79                                                                             0.40                                                                             0.41                                                                             0.29                                                                             0.64                                                                             0.49                                                                             0.50                                                                             0.71                                                                             0.48                                                                             0.47                                                                             0.54 0.67 0.94                          AI      -- -- -- -- -- 6  -- -- -- -- 2    --   ˜4                      wt % Al.sub.2 O.sub.3                                                                 2  <5 -- -- 2  10 12 10 14 13 17   19   2                             MAT                                                                           Conversion,                                                                           73 75 73 77 75 79 75 76 77 77 70   70   74                            wt. %                                                                         C.sub.5 -430°                                                                  39 40 40 41 40 40 39 41 40 39 39   39   41                            Coke    14 12 12 13 13 15 14 13 14 14 10   9    11                            C.sub.4 E/C.sub.4 /T                                                                  0.50                                                                             0.42                                                                             0.42                                                                             0.37                                                                             0.44                                                                             0.40                                                                             0.42                                                                             0.41                                                                             0.40                                                                             0.41                                                                             0.50 0.53 0.49                          __________________________________________________________________________

EXAMPLE 3

Material was prepared as in Example 1, except the after titrating withNH₄ OH, to a pH of 8, the slurry was heated to 52° C. for a totalheating time of about 30 minutes, and filtered. The cake was washed asin Example 1. The syneresis step was accomplished by adding acetic acidto reduce the pH to 4.96. NH₄ OH was added to raise the pH to 5.63. Thematerial was homogenized, aged overnight to a pH of ˜5.57,rehomogenized, and spray dried.

EXAMPLE 4

Material was prepared as in Example 3, except that the slurry was heatedto 81° C. for 47 minutes.

EXAMPLE 5

Material was prepared as in Example 3, except that it was titrated withNH₄ OH to a pH of 5.6, heated to 80° C. over a 30 minute period and heldat 80° C. for 10 minutes.

Comparative Cogel Catalyst Performance and Physical CharacteristicsAfter Steaming

In order to mimic the type of conditions cogels of the present inventionexperience in an FCC process unit, representative cogel was steamed at1450° F. for about 5 hours in 100% steam. To provide comparativeexamples with related cogels in the prior art, tests were also run onthe cogels produce as described in U.S. Pat. Nos. 4,198,319 and4,289,653. Table II, compares the range of characteristics for thesteamed cogels of Example 1-5, with the above-identified patents.

    ______________________________________                                        CHARACTERISTICS OF FEEDSTOCK A                                                ______________________________________                                        Aniline Point, °F.                                                                        181.5                                                      API Gravity        23.5                                                       Nitrogen, ppm      1600                                                       Ramsbotton Carbon, wt %                                                                          0.1                                                        ______________________________________                                    

                  TABLE II                                                        ______________________________________                                        STEAMED COGELS                                                                          Examples 1-5                                                                           U.S. Pat No.                                                                             U.S. Pat No.                                              (averaged)                                                                             4,198,319  4,289,653                                       ______________________________________                                        Surface area                                                                              140-200    176-189    106                                         Pre size dist.                                                                            100-250     69-111    39                                          Pore volume 0.3-0.9    0.4-0.5    0.2                                         % γAl.sub.2 O.sub.3                                                                 <2-20      >29%       ≧14                                  MAT                                                                           Conversion, wt. %                                                                         52-60      52-60      49                                          C.sub.5 -430° F.                                                                   36-40      36-38      35                                          Coke        3-5        3-4        3.1                                         C.sub.4 E/C.sub.4 T                                                                       0.4-0.7    0.5-0.7    0.61                                        ______________________________________                                    

What is claimed is:
 1. A process for catalytically crackinghydrocarbonaceous feedstock, wherein said cracking catalyst consistsessentially of a cogelled, silica-alumina cogel prepared by the methodconsisting essentially of:a. mixing a silicate solution with an aqueoussolution of an acid aluminum salt and an acid, to form an acidifiedsilica sol in said aluminum salt solution, and adjusting said silicasol/aluminum salt solution mixture to a pH in the range of about 1 to 4;b. slowly adding sufficient base with vigorous stirring, to saidacidified silica sol/aluminum salt solution mixture to form a cogelslurry or silica and alumina, and to adjust said slurry to a pH in therange of about 5 to 9; c. aging said cogel slurry at a temperature ofambient to 95° C.; d. adjusting the pH of said cogel slurry to about5-9; e. recovering a cogelled mass form said slurry; f. washing saidcogelled mass; g. adjusting the pH of said cogelled mass to betweenabout 4 and 7, and controlling conditions to induce syneresis to providea cogel having meso and macro pore sizes and a N₂ pore size distributionpeak diameter ranging from about 30 Å to 260 Å; and h. forming saidcombination into particles.
 2. The process as claimed in claim 1 whereinsaid hydrocarbonaceous feed comprises residuum or incremental residuum.3. The process as claimed in claim 2 wherein said residuum containscatalyst-contaminating metals.